I have a chevy 350 +30, with a set of L98 heads. I do not know what the compression ratio is. I am running a Mallory Unilite with a HI6 system/ no-vac advance. The problemis I have to run high octane gas or I get spark knock. I have tried 8 to 12 inital timing and have up to 36degree advance with 12 inital. I assume that this should run under normal pumped gas. I am wondering if I need to get a distributor with a vac advance.